Lady Gaga was playing to an enraptured audience, who were grooving along to the beat of her early hit “Born this Way,” reveling in that giant shot of positivity. The DJ switched to a new disc, and the words and the theme dramatically shifted as Queen’s “Another One Bites the Dust” blared out.
The tone had changed drastically, from manically upbeat to insistently downbeat, but the audience was impervious to that. All that mattered was the driving bump, bump, bump of the rhythm, which the audience continued to headbang to, without missing a beat.
The DJ in this instance was Hirokazu Takahashi, a professor of engineering at the School of Information Science and Technology at the University of Tokyo, and his audience was a group of 10 rats and 20 humans. The rats were fitted with tiny wireless accelerometers, equipment capable of picking up and recording the slightest of head movements, not unlike that of the human listeners, who wore accelerometers on headphones.
Other studies had tried to examine the responses of animals to music, but this highly sensitive equipment enabled the University of Tokyo team to pick up even the most imperceptible shifts of the head.
Hirokazu, an expert in electrophysiology, particularly the electrical activity in the brain, had been studying the auditory cortex to begin to understand why music had such a profound effect on us, and he’d decided to tiptoe into this vast subject by first focusing on rats.
He and his team began the experiment by testing several key assumptions: If the rats responded in any capacity, they would likely do so with a faster beat than humans would enjoy. The scientists also assumed that a recognition of timing in music would be related to the “time constant” of the body. This refers to the time it takes for any physiological process to occur, such as emptying the lungs (about 0.2 seconds in humans).
A natural pace
The body’s time constant for various internal processes differs among individual species and is far faster in small rodents like rats. Think of simply moving; a rat can scramble off far faster than can a lumbering human being.
Takahashi also assumed that the time constant of the brain, the speed with which an organism can respond to physical stimuli, would determine any species’ optimum tempo, and that this neural time constant would also differ among species. He also assumed that the human subjects alone would be keeping time to the music.
After placing the rats in a dimly lit box with a nearby speaker and the volunteers in the human equivalent, a soundproof booth, Takahashi started out by playing one-minute excerpts from Mozart’s Sonata for Two Pianos in D Major (K. 448).
Written when the composer was only twenty-five, the sonata was chosen not only for its rapid, dynamic beat from complex interlocking melodies and cadences, but also because it had been the first piece played in a study that led to the theory of the Mozart Effect.
Researchers at York University in Toronto had demonstrated healing effects by playing the Sonata in D Major to patients with epilepsy—even those in a coma. At the time, the scientists concluded that the effect occurred because the cerebral cortex in both hemispheres of the brain resonated in a healthy way to the architecture of Mozart’s music.
But would rats do the same? Takahashi began playing the Mozart sonata at a normal tempo for a minute. Without conscious effort, the humans began bobbing their heads perfectly in time to the rhythm. This, of course, was expected; humans instinctively sway and move in time to a beat. But what was not expected was the response of the rats, which began bobbing their heads in perfect tempo too.
Takahashi’s team tried slowing down the sonata to 75 percent of normal speed for a minute. The rats and the human volunteers continued to keep time with their bodies, but not as well as they had before. Takahashi then doubled the normal speed for a minute, and then ratcheted it up even further by quadrupling it.
The faster the music was played, the less either humans or rats could rhythmically keep up. Takahashi’s team studied the neural activity of both types of subjects over all four speeds and applied a mathematical model to the data.
The rats have rhythm, too
It turned out that the rats displayed beat synchronicity—meaning when their head bopping was most in time with the music—at one particular tempo. The normal tempo of the Mozart sonata had been 132 beats per minute, which landed squarely in the middle of what turns out to be the rat’s optimal beat speed of 120 to 140 beats per minute.
To the scientists’ astonishment, this Goldilocks speed for a rat was identical to that of the human subjects. Clearly, the rats did not have a brain time unique to their species. It was shared by humans too, which suggested the unthinkable: The animals were processing music in the brain in the same way that we were.
Takahashi and his team also discovered that the rats were even capable of correctly anticipating the beats when the interval between one note and the next was much shorter—as much as one-thousandth of a second.
By the time the team moved on from Lady Gaga and Queen to Michael Jackson’s “Beat It,” and Maroon 5’s “Sugar”—all songs chosen for their similar driving beats—the rats had demonstrated that they were catholic in their musical tastes. Just like us, they instinctively kept time with their heads to the rhythms of every one of the songs.
Takahashi realized the enormity of what he’d just witnessed: The rats were processing music just as humans did.
In a formal press release, Takahashi announced his findings to an astonished scientific community: “Rats displayed innate—that is, without any training or prior exposure to music—beat synchronization most distinctly within 120–140 bpm, to which humans also exhibit the clearest beat synchronization.”
This was huge, the first time a study had demonstrated that animals had innate musical timekeeping that showed up immediately without any training or exposure to music, and it appeared to be identical to that of human beings.
The time constant for the rats’ ability to listen to sounds and music was not the same as the one for their body movement; it was identical to the time constant for people listening to sounds. Even their favorite tempos were the same as those most preferred by human beings.
